Loans and Allowance - Past Due Aging of Loan Portfolio by Loan Class (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	$ 5,095,918	$ 4,641,215
Loans 90 Days And Accruing	112	907
Non-Accrual	29,998	31,389
Total Past Due & Non-Accrual	43,727	52,607
Total	5,139,645	4,693,822
30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	9,490	17,570
60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	4,127	2,741
Commercial and industrial loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,192,079	1,052,275
Loans 90 Days And Accruing	100
Non-Accrual	1,839	4,634
Total Past Due & Non-Accrual	2,567	4,800
Total	1,194,646	1,057,075
Commercial and industrial loans | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	466	166
Commercial and industrial loans | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	162
Agricultural production financing and other loans to farmers
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	78,360	96,884
Loans 90 Days And Accruing
Non-Accrual	1,329	827
Total Past Due & Non-Accrual	1,329	827
Total	79,689	97,711
Agricultural production financing and other loans to farmers | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due
Agricultural production financing and other loans to farmers | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due
Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	415,975	362,084
Non-Accrual	73	736
Total Past Due & Non-Accrual	2,728	4,620
Total	418,703	366,704
Construction | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	2,655	3,884
Construction | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due
Commercial and farmland
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,932,896	1,786,092
Loans 90 Days And Accruing
Non-Accrual	15,754	11,277
Total Past Due & Non-Accrual	20,166	16,829
Total	1,953,062	1,802,921
Commercial and farmland | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	1,385	5,552
Commercial and farmland | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	3,027
Residential
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	725,338	765,634
Loans 90 Days And Accruing	9	502
Non-Accrual	9,523	11,818
Total Past Due & Non-Accrual	13,831	20,471
Total	739,169	786,105
Residential | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	3,664	6,090
Residential | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	635	2,061
Home equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	415,969	344,344
Loans 90 Days And Accruing	3	324
Non-Accrual	1,457	1,952
Total Past Due & Non-Accrual	2,556	4,269
Total	418,525	348,613
Home equity | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	850	1,433
Home equity | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	246	560
Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	76,929	73,990
Loans 90 Days And Accruing		81
Non-Accrual	23	145
Total Past Due & Non-Accrual	550	727
Total	77,479	74,717
Consumer | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	470	445
Consumer | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	57	56
Lease financing receivables, net of unearned income
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	311	588
Non-Accrual
Total Past Due & Non-Accrual
Total	311	588
Other commercial loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	258,061	159,324
Non-Accrual
Total Past Due & Non-Accrual		64
Total	258,061	159,388
Other commercial loans | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due		$ 64